Newbie: module structure and import question

[Ziong]

hi all,
i have question on how to design a module structure.
for example, i have 3 files.
[somewhere]/main.py
[somewhere]/myLib/Base/BaseA.py
[somewhere]/myLib/ClassA.py

main.py
=======
from myLib.ClassA import ClassA

a = classA()
dir(a)

myLib/ClassA.py
===============
from myLib.Base.BaseA import BaseA

class ClassA(BaseA):
   def __init__(self):
       BaseA.__init__(self)
       print "classA"

if (__name__ == "__main__"):
   print "test class A"
   a = ClassA()
   print a


myLib/Base/BaseA.py
===================
class BaseA:
   def __init__(self):
     print "BaseA"


It's fine when i run main.py.
however when i run ClassA.py individually, it would fail in import
statment since the import path is incorrect.
I would like to know is something wrong in my design, or something i
missed.

Also, in practical usage, is that one class in one py file?

thx!

a python newbie